<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        //求1+2!+3!+...+20!的值
        var c = 1;
        var a = 0;
        for (var i = 1; i <= 20; i++) {
            for (var j = 1; j <= i; j++) {
                c *= j;
            }
            a += c;
        }
        console.log("总和是:" + a);
    </script>
</body>

</html>